Regex Match a character which is not followed by another specific character

Question

I\'m writing a CodeMirror extension for Brackets. To defineSimpleCodeMode I need to do some pattern matching and I\'m trying to figure out how to achieve $subject.

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Answer 1

While this seems to be a bad idea, I can see two ways of doing it :

1. Searching for < followed by anything but the % character, then ignoring it

(<)(?:[^%])

The [^] sequence allows you to search for anything but the following character.

The (?:) sequence is for non capturing groups.

2. (Better, if supported) Searching for input not followed by % with a negative lookahead

<(?!%)

The (?!) sequence succeeds if it doesn't match the following character, but is not captured.

If you also want to do it for %>, you can just "reverse" the first option :

(?:[^%])(>)

Or you need a negative lookbehind :

(careful here, the lookahead won't work as you need to go backwards)

(?<!%)>